The present disclosure relates to a storage element which includes a storage layer storing a magnetization state of a ferromagnetic layer as information and a magnetization fixed layer of which the direction of magnetization is fixed, and changes the direction of magnetization of the storage layer with the flow of a current, and a memory device provided with the storage element.
In information equipment such as a computer, or the like, DRAMS with high operation speed and high density are widely used as random access memories.
However, since such DRAMs are volatile memories in which information is lost when the power is disconnected, non-volatile memories in which information is not lost have been demanded.
Therefore, attention has been paid to a magnetic random access memory (MRAM) which records information with magnetization of a magnetic substance as a candidate for non-volatile memories, and development thereof is underway.
An MRAM records information such that current is made to flow on two kinds of address lines (including a word line and a bit line) respectively, which are substantially orthogonal to each other, and magnetization of magnetic layers of magnetic storage elements provided in the junctions of the address lines is reversed by current magnetic fields generated from each of the address lines.
FIG. 12 shows a schematic diagram (perspective view) of a general MRAM.
A drain region 108, a source region 107, and a gate electrode 101, which constitute a selection transistor for selecting each memory cell, are formed respectively in a portion which is separated by an element separating layer 102 of a semiconductor substrate 110 such as a silicon substrate, or the like.
In addition, a word line 105 extending in the front-rear direction of the drawing is provided above the gate electrode 101.
The drain region 108 is formed in the selection transistor in the left-right side of the drawing in common, and a wiring 109 is connected to the drain region 108.
In addition, a magnetic storage element 103 having a storage layer in which the direction of magnetization is reversed is disposed between the word line 105 and a bit line 106 which is disposed in the upper portion and extends in the left-right direction of the drawing. The magnetic storage element 103 includes, for example, a magnetic tunnel junction element (MTJ element).
Furthermore, the magnetic storage element 103 is electrically connected to the source region 107 through a by-pass line 111 in the horizontal direction and a contact layer 104 in the longitudinal direction.
A current magnetic field is applied to the magnetic storage element 103 by making current flow to the word line 105 and the bit line 106 to reverse the direction of magnetization of the storage layer of the magnetic storage element 103, whereby recording of information can be performed.
Then, in order to stably hold the recorded information in a magnetic memory such as an MRAM, or the like, it is necessary for a magnetic layer (storage layer) which records information to have a certain degree of coercive force.
On the other hand, in order to rewrite the recorded information a certain amount of current has to be flowed in the address lines.
However, since the address lines become delicate as elements constituting the MRAM become fine, it becomes difficult to make sufficient current flow.
Hence, as a configuration which enables the magnetization reversal with a smaller amount of current, attention has been paid to a memory configured to use the magnetization reversal by spin injection (for example, refer to Japanese Unexamined Patent Application Publication No. 2003-17782, U.S. Pat. No. 6,256,223, Japanese Unexamined Patent Application Publication No. 2008-227388, PHYs. Rev. B, 54.9353 (1996), and J. Magn. Mat., 159, L1 (1996)).
The magnetization reversal by spin injection is performed such that electrons spin-polarized passing through a magnetic substance are injected to another magnetic substance to bring about magnetization reversal in the magnetic substance.
In respect to a giant magneto-resistive effect element (GMR element) or a magnetic tunnel junction element (MTJ element), for example, the direction of magnetization of at least part of a magnetic layer of such an element can be reversed by making a current flow in the vertical direction of a film surface of the element.
In addition, the magnetization reversal by spin injection is advantageous in that, even when the element becomes fine, the magnetization reversal can be realized without increasing the current.
FIGS. 13 and 14 show schematic diagrams of a memory device configured to use the magnetization reversal by spin injection described above. FIG. 13 is a perspective view and FIG. 14 is a cross-sectional view.
A drain region 58, a source region 57, and a gate electrode 51, which constitute a selection transistor for selecting each memory cell, are formed respectively in a portion which is separated by an element separating layer 52 of a semiconductor substrate 60 such as a silicon substrate, or the like. Among these, the gate electrode 51 also serves as a word line extending in the front-rear direction of FIG. 14.
The drain region 58 is formed in the selection transistor in the left and right sides of FIG. 13 in common, and a wiring 59 is connected to the drain region 58.
In addition, a storage element 57 which includes a storage layer of which the direction of magnetization is reversed by spin injection is disposed between the source region 57 and a bit line 56 which is disposed in the upper portion and extends to the left-right direction of FIG. 13.
The storage element 53 includes, for example, a magnetic tunnel junction element (MTJ element). The storage element 53 has two magnetic layers 61 and 62. Among the two magnetic layers 61 and 62, one magnetic layer is set to a magnetization fixed layer of which the direction of magnetization is fixed and the other magnetization layer is set to a magnetization free layer, that is, a storage layer of which the direction of magnetization changes.
In addition, the storage element 53 is connected to the bit line 56 and the source region 57 respectively through a contact layer 54 in the upper and lower sides. Accordingly, the direction of magnetization of the storage layer can be reversed by spin injection by making a current flow to the storage element 53.
A memory device configured to use the magnetization reversal by spin injection as above has characteristics in that the device structure can be simplified and for this reason high density thereof is possible, in comparison to a general MRAM shown in FIG. 12.
In addition, in comparison to the general MRAM which performs magnetization reversal by an external magnetic field, the memory device is advantageous in that the writing current does not increase even when miniaturization of the element advances, by using the magnetization reversal by spin injection.